Project Summary Pertussis is the most poorly controlled bacterial vaccine-preventable disease in the United States and causes a substantial burden of morbidity and mortality among young infants. The dramatic increase in pertussis incidence in recent years underscores the need for more effective prevention and control strategies. Studies have demonstrated that there are significant sociodemographic disparities in the risk of pertussis infection and morbidity. However, there remains a critical gap in understanding sociodemographic disparities in pertussis. Although it is well established that characteristics of the neighborhood in which one lives can impact health, rigorous investigations of neighborhood-level risk factors for pertussis are sparse and enhanced methodological rigor in simultaneously assessing individual- and neighborhood-level risk factors may contribute to our understanding of sociodemographic disparities in pertussis. Reducing the burden of pertussis on young infants and eliminating health disparities hinges on timely pertussis vaccination. Given documented sociodemographic disparities in vaccination coverage and delay, timeliness of infant pertussis vaccination may be contribute to disparities in disease risk, and therefore, optimization of this prevention strategy is critical. In response to these important gaps in knowledge and the pressing need to effectively optimize prevention strategies, we propose to leverage an opportunity to link several large data sources ? the Philadelphia Department of Public Health immunization registry, clinical disease management system, and vital records database and the U.S. Census Bureau's American Community Survey ? in order to create a population-based cohort of infants born in Philadelphia. This research proposal aims to: 1) determine sociodemographic and neighborhood-level characteristics associated with pertussis; 2) determine sociodemographic and neighborhood-level characteristics associated with delayed pertussis immunization; and, 3) evaluate the effect of an immunization outreach policy change to target late starters of the infant vaccine series on delayed immunization and sociodemographic disparities. Through these analyses, the diversity fellowship applicant will develop a deeper understanding of the association between neighborhood-level risk factors and pertussis, examine sociodemographic disparities in pertussis risk, assess risk factors for delayed infant immunization, and identify opportunities to bolster prevention efforts. This research is proposed in the context of the diversity fellowship applicant completing requirements for a PhD in epidemiology. The degree program will encompass intensive instruction in the fundamentals of epidemiology, biostatistics, data management, and analytic methods. The fellowship will enable additional interdisciplinary training from mentors with expertise in vaccine-preventable disease epidemiology, bioinformatics, immunization policy, and health disparities to contribute to the applicant's development into an independent, scientific investigator and epidemiologist.